The use of bovine fibrin-streptokinase films for the determination of recombinant human plasminogen.

Plasminogen is a key component of the haemostatic system in man and the plasma-derived protein molecule has been actively investigated. Within the last few years cDNA and the gene encoding plasminogen have been cloned and the protein has been expressed in a number of eukaryotic or prokaryotic systems. Yields of expressed plasminogen are frequently low. Currently available assays for plasminogen generally rely on the determination of antigen or utilize tripeptide substrates for measuring functional activity, and they have certain limitations. Assays employing relevant protein substrates offer an alternative way to measure function and overcome the drawbacks associated with the other tests. The use of fibrin films for the assay of low levels of recombinant plasminogen has not been described fully before. The two fibrin film-based assays described in this paper are significant additions to the array of assays available for plasminogen molecules.